Sling 2 with 912 IS propellor options

Model Specific Discussions about the Sling 2 and the Sling LSA.
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glennpretorius
Posts: 18
Joined: Mon Dec 07, 2020 8:55 am
Location: Somerset West, Cape Town

Sling 2 with 912 IS propellor options

Post by glennpretorius »

Anyone who has experience with the 912 IS engine fitted with the Airmaster 3 blade constant speed prop and aluminium spinner with Whirlwind blades on their Sling 2.
glennpretorius
Posts: 18
Joined: Mon Dec 07, 2020 8:55 am
Location: Somerset West, Cape Town

Re: Sling 2 with 912 IS propellor options

Post by glennpretorius »

So I believe 912 is with constant speed option worth looking at. Does anyone have experience with this combination. I am looking at either the 912 IS option for my sling 2 or 914 uls.. Option of really good efficiency with 912IS or impressive climb and cruise performance with 914 ULS. Both really good options. Any advice appreciated
Fly-Fla
Posts: 18
Joined: Sun Feb 23, 2020 8:05 am
Location: North Florida

Re: Sling 2 with 912 IS propellor options

Post by Fly-Fla »

On the Sling facebook page I posted a similar question a while back. Someone ( I think Adam at Midwest Panel Builders) said there was very little gain from the constant speed prop on the 912 engine in s Sling 2. What I did get good feedback on was adding the 914 turbo engine and constant speed prop. Evidently that is a sporty combination but does add a good bit of cost to the sling 2 project.
glennpretorius
Posts: 18
Joined: Mon Dec 07, 2020 8:55 am
Location: Somerset West, Cape Town

Re: Sling 2 with 912 IS propellor options

Post by glennpretorius »

Very interesting, thank you. It seems that the only real advantage of the 912 IS with constant speed prop would be fuel efficiency. The extra performance of the 914 UL has me leaning towards the 914 option with the same option of constant speed prop.
glennpretorius
Posts: 18
Joined: Mon Dec 07, 2020 8:55 am
Location: Somerset West, Cape Town

Re: Sling 2 with 912 IS propellor options

Post by glennpretorius »

Feedback on my Sling 2 fitted with 912 IS sport and Airmaster constant speed prop whirlwind blades:

Having done some 75 hours on the aircraft and both short and long flights i established the following...

Aircraft weight 700 kg at take off
FL 095 ISA +10
TAS 120 kts
Climb selection on prop controller - gives around 5400 rpm, i dont use cruise setting
Throttle 21.3 MAN PRESS - approx. This i need to explain as i established this by slowly reducing the power whilst observing the fuel flow which typically is about 20 litres per hour . You will find a throttle position where the fuel flow suddenly reduces to around 15 or 16 litres per hour.

I found that this gave me 120 to 122 TAS
NB: in the above example , at full throttle i cruise between 127 and 132 TAS

I have just completed two 5h00 flights , 150 ltrs fuel on board, 2 persons on board with luggage so pretty close to 700 kg and average fuel consumption 17.3 litres per hour using the method of throttling back the engine until the fuel flow suddenly reduces as mentioned above .

What would be interesting is to leave full throttle ( climb power) at top of climb and cruise at the higher TAS . of 130 at 20 lph. Although basic maths i guess suggest that a fuel flow reduction of 20 % against a speed increase of roughly 10% leans favourably towards the fuel benefit of reducing the throttle setting slightly .. .....

So its probably cheaper to fly thsn drive....
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